Insufficient roof ventilation can result in a prolonged interface between still moist air and a colder surface. Moisture condensation on the colder surface occurs when these conditions are present. The condensed moisture often spots and damages ceilings. In more severe cases, structural members such as rafters, truss chords, joists and studs are continually damp and become unsound. Buildings with insufficiently ventilated roofs also tend to be warmer in summer months due to the presence of solar-heated air trapped within. Because of the heat retained by inadequately ventilated roofs, these buildings are more expensive to maintain at comfortable temperatures than if these roofs were adequately ventilated. However, when adequate ventilation occurs, air is kept in motion by being circulated from outside the roof, through the attic, and out through vents often placed at or near the roof ridge. Such ventilation is continually necessary in order to prevent accumulation of hot air or condensed moisture.
Various products have been developed to provide forms of ventilation. These products either provide separate ventilation structures or are themselves building materials with ventilating properties.